The circadian system synchronizes daily with the day–night cycle of our environment. Disruption of this rhythm impacts the emergence and development of many diseases caused, for example, by the overproduction of free radicals, leading to oxidative damage of cellular components. The goal of this study was to determine the activity of superoxide dismutase (SOD), glutathione peroxidase (GPx), catalase (CAT), glutathione transferase (GST), glutathione reductase (R-GSSG), and the concentration of glutathione (GSH) in the circadian rhythm. The study group comprised 66 healthy volunteers (20–50 years; 33 women; 33 men). The blood was collected at 2, 8 a.m., and 2, 8 p.m. All samples marked the serum melatonin concentration to confirm the correct sleeping rhythm and wakefulness throughout the day. The activity of study enzymes and the concentration of GSH were measured by the spectrophotometric method. Confirmed the existence of circadian regulation of oxidative stress enzymes except for GST activity. The peak of activity of study enzymes and GSH concentration was observed at 2 a.m. The increased activity of enzymes and the increase in GSH concentration observed at night indicate that during sleep, processes allowing to maintain of the redox balance are intensified, thus limiting the formation of oxidative stress.

Pregnancy predisposes to thrombotic hemostasis, reflected in the laboratory as, e.g., increased levels of D‐Dimers and fibrinogen, but in physiological pregnancy, the risk of venous thrombosis does not increase. Risk may increase if gestational diabetes mellitus (GDM) or nicotinism coexists. Study aims were to determine reference values ​​for D‐Dimers and fibrinogen concentrations in each trimester of pregnancy, corrected for GDM and nicotinism. Subjects and Methods. The study involved 71 pregnant women aged 25‐44 y. Venous blood was collected three times: in the first (11‐14 weeks), second (20‐22 weeks), and third (30‐31 weeks) trimesters. D‐Dimer concentrations were determined by an enzyme‐linked fluorescence assay, fibrinogen concentrations by a coagulation method according to Clauss. Results. Significant increases in D‐Dimers and fibrinogen concentrations were observed, increasing with successive trimesters (p ANOVA < 0.0001). Furthermore, a positive correlation between D‐Dimers and fibrinogen was detected in the second trimester of pregnancy (r = 0.475; p < 0.0001). In addition, a significantly higher fibrinogen concentration was found in women with GDM compared to without GDM (p = 0.0449). Reference ranges for D‐Dimers were established, in trimester order, as follows: 167‐721 ng/mL, 298‐1653 ng/mL, and 483‐2256 ng/mL. After adjusting for risk factors, significantly higher D‐Dimer values ​​(mainly second and third trimesters) were obtained: 165‐638 ng/mL, 282‐3474 ng/mL, and 483‐4486 ng/mL, respectively. Reference ranges for fibrinogen were, in trimester order, 2.60‐6.56 g/L, 3.40‐8.53 g/L, and 3.63‐9.14 g/L and, after adjustment for risk factors, 3.34‐6.73 g/L, 3.40‐8.84 g/L, and 3.12‐9.91 g/L. Conclusions. We conclude that the increase in D‐Dimers and fibrinogen levels in women with physiological pregnancy was compounded by gestational diabetes (GDM) and nicotinism. Therefore, D‐Dimers and fibrinogen pregnancy reference values require correction for these risk factors.